Client devices and/or proxy servers receive web page data from host servers and, in many cases, cache the data. For example, the first time a device accesses a particular web page, it may cache the data locally so it can load the web page faster in the future. However, the host server may update the web page, causing the cached data to become stale. In some cases, the client device and/or proxy server may continue to use the cached web page even after the host server has updated the web page, delivering outdated information to the end user.